Acceleration of the growth of farm animals at a lower cost per 1 kg of weight gain is one of the main problems of stock raising. It is known that the productivity of farm animals can be increased by giving them somatostatin, some anabolic hormones or antibiotics. However, the high cost of somatostatin does not always make this method profitable, and furthermore, the use of hormonal preparations especially anabolic ones in the production of foodstuffs is not received with enthusiasm by the public. For these reasons somatotropic preparations have not yet found wide use in stock raising and anabolic hormones are prohibited in animal husbandry. However, it is possible to increase the concentration of endogenic anabolic factors by acting on their inhibitor--somatostatin, which has good prospects for use in agriculture and in medicine (Muromtsev G. S. et al., 1990, "Basics of agricultural biotechnology", Agropromizdat, Moscow; Reichlin S., ed., 1987, Somatostatin, Basic and Clinical Status, Plenum Press, New York, Weil C., ed., 1992, Basic and Clinical aspects of neuroscience, v. 4 Somatostatin, Springer-Verlag; Spencer G. S., 1985, Hormonal systems regulating Growth, Review, Livestock Production Science, 12, 31-46).
Somatostatin, a biologically active tetradecapeptide having the following amino acid sequence--AGCKNFFWKTFTSC, is produced in the hypothalamus and the gastrointestinal tract. The sequence of somatostatin-14 is highly conservative among vertebrata, while in mammals in general it does not have a specific species. Somatostatin has a strong inhibiting effect on a large number of hormones and related thereto functions of the organism: somatostatin, the thyrotrophic hormone, insulin, glucogen, secretin, gastrin, pepsin, maletin and a number of regulatory peptides. The wide range of action of somatostatin on the factors necessary for growth and utilization of food provides a good outlook for its use as a means for controlling the growth of animals, for reduction of expenditures on foodstuff, etc. Therefore, the autoimmune reaction to somatostatin, resulting in a reduction of the concentration of this peptide in the blood, and a result induction of anabolic factors and acceleration of the growth of the animals, is one of great interest. Active or passive immunization of animals, as a result of which antisomatostatin antibodies (Reichlin, 1987; Spencer, 1985; Baile C. A. et al.) The neurophysiological control of growth, In: Control and Manipulation of Animal Growth, Buttery P. J. et al., ed., 1986, Butterworths, London, pp. 105-118) appear in the blood, is used to reduce the concentration of endogenic somatostatin.
Somatostatin is a low-molecular protein-hapten, its half-life in the blood stream is several minutes. In view of this somatostatin conjugates with various proteins are used for immunization with somatostatin. It should be underlined that this approach makes it possible to obtain ecologically pure food products, since it does not include the use of any preparations of direct hormonal effect or antibiotics, but is based on small changes in the concentration of endogenous protein anabolic factors, characteristic for elite, highly-productive animals (Reichlin, 1987; Buttery et al., 1986).
A large number of studies have shown that animals immunized with somatostatin have an average daily weight gain of 10-20%, an appetite reduced by 9% and an 11% increase in the efficiency of food utilization. Wherein improved absorption of food components and a slower passage of food through the gastrointestinal tract with sluggish peristalsis is observed. Animals immunized with somatostatin, and also their offspring, have correct proportions, and the distribution of the weight of the animals between the muscles, bones and fat is the same as in the control (Reichlin, 1987). Immunization of gestated goats results in an increase in the weight of newly-born by 10% and an increase in milk yield.
However, the wide use of somatostatin-14, in particular, to stimulate the growth of animals by means of immunocorrection using antisomatostatin antibodies (Muromtsev G. S. et al. and Reichlin, 1987) is not possible because of its high price, since the main way to obtain somatostatin is by chemical synthesis (38 U.S.A. dollars for 1 mg of a somatostatin preparation, Sigma catalog, U.S. A., 1992), and this does not make it possible to realize this approach in practice from an economical point of view. The development of gene engineering methods has made it possible to prepare a number of protein and peptide hormones by synthesis in the cells of microorganisms. However, it is not possible to effect the direct microbial syntheses of somatostatin using recombinant DNA technology because of its small size (14 amino acid residues) (Itakura R. et al., 1977), "Expression in E. coli of a chemically synthesized gene of the hormone somatostatin", Science, 1986, 1056-1063). Several methods for obtaining somatostatin in the form of chimeric proteins with subsequent specific cleavage of the product of interest have been described (Itakura R. et al., 1977; Russian patent application No. 4921158/13 of Mar. 26, 1991).
The first research in respect of obtaining somatostatin-14 by use of gene engineering technology was conducted in 1977 by Itakura. The authors constructed a hybride gene on the basis of .beta.-galactosidase E. coli, in the C'-end region of which a chemically synthesized sequence of somatostatin is engineered. Later, effective producers of chimeric proteins were created on the basis of that process with a sequence of somatostatin introduced into chimeric trpE, trpD and recA E. coli genes. The level of expression of chimeric proteins reached 15-30% of the total amount of proteins, while the output of the somatostatin approached the requirements of industrial production (Itakura R. et al.).
A recombinant plasmid DNA encoding somatostatin and a strain E. coli--a producer of somatostatin, are taught in Russian patent application No. 4921158/13 with priority from Mar. 26, 1991. The claimed plasmid determines the constitutive synthesis of a hybride protein of chloramphenicol acetyl transferase-somatostatin-14 under the control of its own promoter in cells of E. coli MKD3207 with a reduction of the level of degradation of anomalous proteins. However, the gene engineering constructions described above ensure the preparation of chimeric proteins, the immunogenic activity of which with respect to somatostatin is extremely low, and therefore these proteins are not yet being used in agriculture or medicine.